1. Field of the Invention
The present invention relates to a transmit/receive switch which allows a millimeter wave antenna or antenna system to be shared for use by both a transmitter and by a receiver.
2. Description of Related Art
Modern wireless communications systems require transceivers that deliver gigabit speeds, are smaller in size, and have lower power consumption and cost. This motivates research to develop transceiver-on-chip and transceiver-in-a-package technologies. Recent advances in millimeter wave electronics have meant that significant portions of the system can now be integrated onto a single substrate or package. In order to achieve low costs and high digital integration, the complementary metal-oxide-semiconductor (CMOS) fabrication process is the process of choice as CMOS is the standard and a cost effective process for building digital circuits. Unfortunately, compared to other much more expensive processes such as SiGe and GaAs, CMOS has greater process variability, lower carrier mobility constants, and smaller device breakdown voltages. This makes the design of millimeter wave wireless transceivers on a CMOS chip particularly challenging.
Rather than having two separate antennas with one antenna used exclusively for transmitting and the other antenna used exclusively for receiving, one way to reduce the size of a transceiver is to use a transmit/receive (T/R) switch to selectively connect both a transmitter and a receiver to a single antenna. Eliminating one antenna saves substantial space. However, T/R switches must be a high performance component as transmitted signals are often magnitudes of order more powerful than received signals, meaning that even slight leakage of transmit signals to the receiver circuitry could saturate the receiver circuitry. Consequently, high isolation must be provided by the T/R switch.
The lossy and relatively poor performance of CMOS makes T/R switch isolation very difficult to achieve, particularly at millimeter-wave frequencies. Consequently T/R switches at RF or millimeter wave frequencies are usually built as a discrete component on gallium-arsenide and P-I-N diode technologies. However these technologies make costs much higher, make integration with other CMOS circuitry difficult, and do not permit system-on-a-chip in CMOS. T/R switches might also be made using integrated bipolar junction transistor and CMOS (BiCMOS) technologies, or silicon on insulator (SOI) technology, however these also raise costs relative to CMOS processes.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.
Throughout this specification the word “comprise,” or variations such as “comprises” or “comprising,” will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.